The present invention relates to a system for sensing and evaluating the rotation of the auxiliary drive of a utility vehicle.
A self-propelled utility vehicle typically includes a main drive engine, a gearbox for the propulsion drive and an auxiliary drive to which an implement or assembly of appliances can be selectively connected. The power output of the main drive engine is branched into a first part for the propulsion drive and a second part for the auxiliary drives. A rotational speed sensor senses the rotation of the auxiliary drive.
With self-propelled utility vehicles with power take-off drive such as, for example, agricultural tractors, neither the drive-line driving the vehicle nor the power take-off shaft drive may be overloaded by the power output produced by the main drive engine. Therefore the engine power output is limited in such a way that an overload of the drive-line or of the power take-off shaft drive can occur neither for a pure propulsion drive nor for a pure power take-off shaft drive. However, if the main engine power output is applied simultaneously to the vehicle propulsion drive as well as to the power take-off shaft drive, so that a part of the power output is transmitted to the wheels and another part of the power output to the power take-off shaft, the engine power output can be increased further (power boost), without overloading the drive-line or the power take-off shaft drive.
For this purpose EP-A-0 901 928 proposes measurement arrangements for the determination of a power limiting value in the auxiliary drives and in the propulsion drive and to have the power output of the main drive engine conform to each of the power limiting values on the basis of the values so determined. The power limiting value is then detected as the torque of an auxiliary drive, a hydraulic pressure or the deflection of a control lever. However, the measurement of these values requires additional sensors and an increased measurement cost.
It is desirable to determine automatically and by simple means whether an auxiliary drive is connected to an assembly of appliances and is active. With such information, for example, the power output of the main drive engine can be controlled in a corresponding manner or other values applied.
Accordingly, an object of this invention is to provide a system and method for determining automatically whether an implement or appliance is connected to an auxiliary drive by sensing and evaluating the rotation of an auxiliary drive.
This and other objects are achieved by the present invention, wherein a sensor senses rotation of an auxiliary drive and an evaluation unit determines the intensity of the second harmonic of the sensor signal and transmits corresponding control signals as a function of a pre-determined threshold value.
It has been found that an auxiliary drive, such as a power take-off shaft drive, performs torsional vibrations with characteristics harmonic vibrations, as long as an implement is connected to and driven by the auxiliary drive. A particularly prominent frequency of these torsional vibrations is twice as high as that corresponding to the basic number of revolutions of the auxiliary drive. If the auxiliary drive is operated without an attached implement this second order torsional vibration does not appear or does so only to a very weak degree. The invention monitors this second order vibration (second harmonic) and determines whether or not an implement is connected to the auxiliary drive. The system may actuate a warning light to indicate to the operator that a device is connected to the power take-off shaft.
When an attached implement is connected to and driven by the auxiliary drive, the auxiliary drive absorbs power. Due to the unavoidable friction losses in bearings and the like, at least an idling power loss is absorbed by the auxiliary drive, even if the attached implement is not operating but is merely carried along. This idling power loss can amount to 10% of the main drive engine power output.
The information whether or not an attached implement is connected to the auxiliary drive is utilized to increase the maximum permissible engine power output (power boost), as long as an attached implement is connected. The engine is normally operated at a maximum power output at which the drive line is not overloaded in pure propulsion operation. If the invention determines that an implement is connected, then the maximum power output of the main drive engine is automatically increased by, for example, 10%, by increasing the amount of fuel injected by the fuel injection pump by a corresponding amount.
The present invention senses only the presence of an attached implement, without regard to the actual power absorption of the implement. Thus, no pressure sensors, force sensors or torque sensors are required. Instead, an auxiliary drive rotational speed sensor signal, that is usually present anyway, can be utilized for the evaluation. Thus, fewer sensors are required than with other processes. No sensor calibrations are necessary. Existing drive-lines or auxiliary drives can be retrofitted by very simple means, without the need for extensive modifications. It is only necessary to evaluate the signal of an auxiliary drive sensor, that is already present, and this requires only the addition of a relatively simple program to the algorithm performed in the evaluation unit. The algorithm can be integrated into the electronic engine control and operates very efficiently with respect to power.
In order to avoid an overload of the auxiliary drive in case the vehicle is stationary and the drive-line does not absorb any power, a preferred further feature of the invention monitors the drive-line rotational speed or the vehicle speed. The engine power output can be increased beyond a normal maximum power limit (power boost) only if a minimum rotational speed of the drive-line or a minimum vehicle speed is exceeded.
Preferably, means are provided for the detection of the rotational speed of the auxiliary drive or the time interval (period) between successive sampling pulses. From the changes in the rotational speed or the change in the time intervals the amplitudes or the intensities of the particular rotational speed variation are calculated which have twice the frequency (second harmonic) of the basic rotational speed of the auxiliary drive. The determination of the intensity of the second harmonic is preferably performed by a narrow band filter, which filters the second harmonic from the sensor signal.
Preferably, the sensor signal is evaluated by an electronic data processing unit. This does not require any specially configured electric control circuits, but merely the programming of an evaluation unit. The determination of the magnitude of the second harmonic is most appropriately performed by a Fourier transform.
Preferably, the magnitude of the second harmonic is compared to a predetermined threshold value. When the threshold is exceeded a signal is transmitted to indicate that an implement or assembly of appliances is connected to the auxiliary drive. This indication can be performed visually or acoustically and, among other purposes, provide increased operating safety.
The utility vehicle includes a main drive engine, a gearbox for the propulsion drive and at least one auxiliary drive to which an implement can be selectively connected. The power output of the main drive engine is branched to a first part to the propulsion drive and to a second part to the auxiliary drives. At least one auxiliary drive sensor, for example, a rotational speed sensor, monitors the rotation of the auxiliary drive. An evaluation unit as described above, detects the second harmonic of the sensor signals and determines whether these exceed a predetermined threshold value. Preferably the auxiliary drive includes a power take-off shaft to which an implement can be connected by a universal joint, because it has been found that the second harmonic is particularly distinctive when a universal joint is connected with a slight angularity to the power take-off shaft drive.